This invention relates to an ignition system for an internal combustion engine and more particularly to an ignition system that insures against kick back or reverse rotation from occurring during initial engine start up.
There is disclosed in our co-pending application Ser. No. 10/605,843, filed Oct. 30, 2003, based upon Japanese Application Serial Number 2002-342256 and assigned to the assignee hereof an ignition system that is designed to prevent reverse rotation commonly called “kick back” upon engine starting by detecting a condition where engine speed starts do decrease after the starting operation has begun by disabling the continued ignition until another starting operation has begun.
However that system has a disadvantage as may be best understood by reference to FIGS. 1–3. FIG. 1 illustrates the relevant portion of the engine and its ignition system. As seen in this figure, a shaft of the engine such as its crankshaft 11 or any other shaft that rotates in timed relation to the crankshaft has formed on its peripheral surface a timing mark 12 that has a predetermined circumferential length between its leading edge A and its trailing edge B. This circumferential length may be in any desired range, normally in the range of 30 to 60 degrees.
Cooperating with this timing mark 12 is a sensor 13 of any known construction that is utilized to provide a signal that is transmitted to an ignition system, not shown in these figures. but which will be described in more detail later by reference to the remaining figures that illustrate preferred embodiments of the invention.
The sensor 13 comprises normally a core 13a around which a coil 13b is wound to produce a pulse signal as shown in FIGS. 2 and 3 as the shaft 11 rotates and the leading and trailing edges A and B pass. The arrow R indicates the normal rotational direction of the shaft 11. The first generated pulse is positive while the second is negative regardless of the direction of rotation.
There may be two modes of reverse rotation in which the engine rotates in reverse after the leading edge A of the projection 12 faces and passes by the core 13a. One of these occurs before the trailing end B leaves the sensor core 13a (in-projection-reverse rotation). The other (out-of-projection reverse rotation) occurs after the trailing end B leaves the sensor core 13a but before top dead center is reached.
FIG. 2 shows the pulse waveform in the in-projection reverse rotation mode. In the normal rotation state during cranking for starting the engine, a rise-up pulse (positive pulse) is produced when the fore-end A of the timing mark is detected by the pulser coil 13 for each rotation of the crankshaft, followed by a decay pulse (negative pulse) when the trailing end B of the projection is detected. When reverse rotation is about to occur, the rotation of the crankshaft slows down gradually. When the rotation speed becomes zero after the pulser coil 13 detects the fore-end A of the timing mark 12 somewhere in the position before reaching the trailing end B and thereafter reverse rotation occurs.
Thus when the leading end A of the timing mark 12 again passes by the detection core 13a of the pulser coil 13 after starting reverse rotation, a decay pulse (negative pulse) is produced from the same end A of the timing mark 12. However, the output of the generator decreases due to a decrease in the crankshaft rotation. In accordance with the metholodgy of the aforenoted co-pending application, the reverse rotation of the crankshaft 11 is detected from the decrease in the generator output.
In response to this, an ignition prohibiting signal is given out. As a result, even if the negative pulse is given out the leading end A of the timing mark 12 the ignition signals are prohibited. Thus, if the engine misfires, no combustion occurs in the reverse rotating direction, and kickback is prevented from occurring.
As described, the kickback is prevented from occurring by prohibiting ignition during reverse rotation and the crankshaft 11 will stop rotating. After that, in order to permit re-starting the engine by cranking, the ignition prohibiting state must be cleared. This is done in the aforenoted co-pending application by clearing the ignition prohibiting state upon the input of a first positive pulse. After that, when the trailing end B of the timing mark 12 is detected and a negative pulse is produced, ignition signals are permitted and combustion occurs for the normal rotation of the engine.
FIG. 3 shows the pulse waveform in the out-of-projection reverse rotation. In the normal rotation state during cranking for starting the engine, like the situation of FIG. 2, the fore-end A of the projection is detected for every rotation of the crankshaft and a rise-up pulse (positive pulse) is produced, then a decay pulse (negative pulse) is produced when the trailing end B of the timing mark 12 is detected.
If the rotation speed of the crankshaft gradually slows down and the reverse rotation is about to occur, the leading end A of the timing mark 12 is detected and the timing mark 12 slowly passes by the detecting core 13a of the pulser coil 13. Subsequently the trailing end B passes by the detecting position 13a and produces a pulse indicated at 14. Here, the rotation speed of the crankshaft 11, when it is low, may becomes zero before the trailing end B reaches the top dead center and the crankshaft 11 will turns in reverse.
As a result, the trailing end B of the timing mark 12 that has once passes by the detecting core 13a of the pulser coil 13, returns to the detecting core 13a, and is detected to produce a positive pulse 15.
Subsequently, when the leading end A of the timing mark 12 passes by the detecting core 13a, a negative pulse 16 is produced. Also this out-of-projection reverse rotation, like the situation shown in FIG. 2, is detected from the decrease in the output of the generator, and ignition is prohibited to prevent kickback from occurring after the reverse rotation occurs.
However and as described above, because the ignition prohibiting state is reset by cranking again after the stop of the crankshaft rotation, ignition prohibition is cleared by the first positive pulse 15 produced after the reverse rotation. Therefore, when the projection end A is detected and a negative pulse 16 is produced after that, ignition signals are given out. Thus rather than preventing reverse rotation, the engine may continue to operate in reverse.
In view of these potential problems it is a principal object of this invention to provide a kickback preventing apparatus and method that is effective to rapidly detect a reverse rotation operation during starting and prevent further reverse rotation by positively preventing ignition and in particular to reliably prevent kickbacks from occurring in the out-of-projection reverse rotation.